This invention relates to a Liquid Crystal Display of the X-Y matrix type containing auxiliary repair lines which can be selectively shorted to an open circuited main address line. More particularly, it relates to auxiliary repair lines which may be driven from either end thus doubling the number of address line repairs that can be effectuated for any given amount of repair lines.
U.S. Pat. No. 4,688,896 issued Aug. 25, 1987, assigned to the General Electric Company the assignee of the present invention, describes a Liquid Crystal Display device of the X-Y matrix type with line repair capability by means of auxiliary address lines which may be selectively shorted to any main address line having an open circuit so that the open circuited address line may then be driven from the auxiliary repair line. Thus, improvements in manufacturing yield for Liquid Crystal Displays having very high address line desities (i.e., densities in the order of 100 or more per inch) may be realized because any open circuit main address line failure occurring during manufacture may be readily repaired by electrically shorting an open circuited address line to the auxiliary line. The open circuited address line is then driven from the auxiliary line.
Separate auxiliary address repair lines cross all of the main X address lines and all of the main Y address lines so that any open circuited main address line in the matrix may be repaired by electrically shorting an auxiliary repair line to that address line. Since an open circuited address line will, depending on its location, de-energize all of the pixels beyond the open circuit the ability to repair the address lines is highly advantageous in a high density display. Thus, in a 4".times.4" display with a hundred line per in. density there are at least 400 X address lines and 400 Y address lines, and loss of a single address line can result in deenergizing anywhere from 1-400 pixels. The invention described in the above identified patent is extremely useful in permitting repair of any address lines found to contain an open circuit thus enhancing the overall manufacturing yield. The ratio of auxiliary address repair lines to address lines can be kept quite low (1:10 or less). For example, for a 4.times.4 inch matrix addressed display having 400 X and 400 Y address lines, 32 address repair lines( 16 ; on either side of the active matrix area) for each of the maix X and Y address line groups has been found adequate.
In the system shown in U.S. Pat. No. 4,688,896, the auxiliary repair lines are single ended in that they contain a single drive pad at one end of the repair line for receiving the driver signals to energize the main address line whenever a repair is effected. Thus, when a when the repair line is shorted to a main address line, the portion of the repair line beyond the point of repair is not usable and is, in effect, wasted. It would be desirable and very useful to reduce the total number of auxiliary repair lines without diminishing the repair capacity. Reducing the number of line permits wider spacing of the lines thereby minimizing the possibility of shorts between the repair lines. Furthermore, it permits the use of wider repair lines with the attendant reduction in the resistance of the repair lines; and it minimizes the non-active area and hence the overall size of the Liquid Crystal Display.